It is often desirable in metallurgy to combine certain elements for the purpose of producing an alloy of favorable properties. However, it is sometimes extremely difficult to dissolve the alloying elements quickly or reach complete homogeneity in a reasonable period of time. This is particularly the case with the alloying of aluminum with titanium. Titanium has been added to aluminum in order to reduce the grain size and improve the performance of cast aluminum products. Aluminum-titanium alloys often have improved mechanical properties, increased crack resistance, and enhanced surface uniformity, primarily because of the reduction in grain size. The titanium can be added to the aluminum in the form of elemental titanium, titanium salts, or any of a number of titanium alloys.
The major problem with regard to titanium-aluminum alloying is that a significant amount of the titanium forms into compounds such as TiAl.sub.3 which grow out in dendritic patterns and form layers which must be further broken up. A mechanism for this incorporation of titanium into aluminum has been proposed in Machowick et al., Journal of the Less Common Metals, 1, 456-66 (1959). It was suggested that a very thin TiAl.sub.3 layer forms and that TiAl.sub.3 particles continue to grow out from this original layer. It was also concluded that this layer forms faster than the rate of diffusion of aluminum into titanium, and that the reaction is strictly a surface reaction. It is for this reason that adding titanium to aluminum by current methods involves significant delay in the casting procedure necessary for dissolution and diffusion of the titanium. It is thus desirable to develop a process to promote a fast and homogeneous alloying of titanium and aluminum.
Ultrasonic energy is a widely used tool in the field of metallurgy. Ultrasonic devices, such as those described in U.S. Pat. Nos. 2,820,263 and 3,162,908, are employed for a number of purposes in this industry. For instance, ultrasound treatment has been used to relieve residual stress in metallic welds, as described in U.S. Pat. No. 3,274,033, to refine the structure of superplastic zinc base eutectoids (U.S. Pat. No. 3,542,607), disperse inert particles in a molten matrix (Fairbanks, IEEE Transactions on Sonics and Ultrasonics, 14, 53-59 (1967)), and to reduce the grain size of stainless steels (Lane et al., Transactions of the Metallurgical Society of the AIME, 218, 985-990 (1960)). However, heretofore, ultrasonic energy has not been applied to enhance difficult metal alloying procedures such as the dissolution of titanium into aluminum. It would be of great value to develop a method by which ultrasonic energy could be used in order to promote the dissolution of titanium in the preparation of titanium-aluminum alloys.